In one conventional technique for the manufacture of thin film integrated circuits, a relatively thin layer of patterned insulating dielectric film is grown or deposited on one or both surfaces of a slice of semiconductor material. To define those areas on the semiconductor slice where it is desired to generate semiconductor features, a layer of photoresist material is spun on to the insulating layer, and is subsequently exposed through a mask.
After exposure of the photoresist material through the mask, the layer of photoresist is developed and processed by means of a suitable solvent, exposing select areas of the underlying layer. A wet acid-based dip is then used to etch the insulating layer from the surface of the semiconductor slice in the exposed areas, the remaining photoresist material serving as an etch-mask for the surface covered by it. Following the wet etching process, a water rinse and a drying step are implemented. The remainer of the photoresist material is subsequently removed, followed by an acid dip required for the removal of inorganic residues.
There are a number of disadvantages with the etching step used in this particular technique, including physical degradation of a photoresist etch mask; finite chemical degradation of a metallic etch mask; enhanced undercutting effects creating undesirable slopes of the etched channel; severe chemical degradation of underlying layers; required post-etch water rinse and drying steps which reduce production yields; short shelf-life of etching solution due to contamination; and it is generally very hazardous to personnel and undesirably polluting.
In an attempt to overcome these problems, other prior art techniques utilize a gas mixture for the generation of a plasma. For example, U.S. Pat. No. 4,028,155 to Jacob discloses a plasma process and material for chemically etching a metal, wherein the gaseous plasma is formed from a mixture of oxygen, a halogen containing gas selected from designated groups, and a halocarbon vapor or gas having no more than two carbon atoms per molecule with at least one of the carbon atoms linked to a predominance of chlorine atoms. The inclusion of oxygen in the mixture is disadvantageous, however, because the oxygen actively combines with and etches the organic photoresist. The loss of photoresist is undesirable.
U.S. Pat. No. 3,518,132 to Glendinning is directed to a vapor etching process wherein the combined vapors of hydrogen fluoride and of nitrous oxide are applied to a metallic surface causing corrosion. The corrosion is then dissolved in sodium hydroxide leaving an etched surface. However, this patent relates to vapor and liquid etching as opposed to plasma etching. Moreover, hydrogen fluoride is a corrosive, toxic acid that is difficult to handle and would not be expected to have the same properties as fluorocarbons which are inert and non-toxic.
U.S. Pat. No. 4,292,153 to Kudo et al. discloses a method for processing substrate material by plasma treatment in a reaction chamber, having the steps of mounting the substrate materials onto a series of electrode plates arranged in parallel to each other, connecting alternate ones of the electrode plates to alternate ones of a pair of bus lines, applying high-frequency power between the pair of bus lines for producing plasma between the electrode plates, and changing the feedpoints of the high-frequency power on the pair of bus lines so that the plasma treatment is effected substantially uniformly in the spaces between the electrode plates. The patent discloses the use of a reaction gas of nitrous oxide, nitrogen, monosilane, ammonia, or carbon tetrafluoride, but there is no suggestion that the nitrous oxide and carbon tetrafluoride be combined and used as a mixture without any other gaseous components.
U.S. Pat. Nos. 4,209,349, 4,243,475 and 4,264,382 disclose processes wherein nitrous oxide is used in methods for depositing silicon dioxide, and not for etching silicon dioxide. Also, these patents do not disclose the use of fluorocarbons.
U.S. Pat. Nos. 4,028,155, 3,951,709, 3,951,843, 3,867,216 and 3,654,108 relate to etching with fluorocarbons, but do not discuss the use of nitrous oxide as a component in the gas mixture.